# Proper Attic temperature setting



## DoWhat

> How much attic ventilation is required to provide proper temperature and moisture control? A number of studies sponsored by federal energy funds are under way to look at ventilation rates and methods. However, several studies previously made can help with this decision. The maximum ventilation rate is required to remove heat during the summer cooling months. Attics can reach temperatures of 150 to 160 degrees F during a summer day, although outside air temperatures are only 95 to 97 degrees F. The cooling load for a home air conditioner depends on the difference in temperature between the inside and outside air, and reduction of attic temperatures from 155 degrees to 105 degrees F will result in a significant reduction in cooling load. In a home with poor ceiling insulation, heat movement through ceilings may account for 30 percent or more of the total cooling cost. With a well-insulated ceiling, this source of heat may account for only 12 to 15 percent of the total cooling cost. Thus, high attic ventilation rates are most important for poorly insulated ceilings. A poorly insulated ceiling is one whose R rating is less than 14 or one with fewer than 4 inches of fiberglass, rockwool or cellulose insulation.
> 
> Attic temperature depends on the amount of solar radiation, construction details and the rate of ventilation. Calculations indicate that on a July day in Texas, a ventilation rate of one air change per minute for a typical attic using 95-degree F air will lower the peak attic temperature to about 101 degrees F. Providing half air change per minute will lower the temperature to about 106 degrees F. Thus, the first half change per minute is most effective and a doubling of this rate only achieves about 5 degrees F additional cooling. Studies indicate that further increases in ventilation are not effective in significantly reducing attic temperatures.
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> Winter attic ventilation must be sufficient to remove moisture vapor moving from the living space to the attic. In general, ventilation adequate for summer cooling is more than adequate for winter ventilation. Winter rates need not be more than about a tenth of the summer rate.
> 
> *Calculate the required summer ventilation rate by determining the volume of attic space and dividing by 2. This will be the cfm (cubic feet per minute) of ventilation air needed. The volume is determined approximately for a rectangular house by multiplying the height from the ceiling to the peak/ridge (H) times the width of the house (W) times the length (L) and dividing by 2 -- ( H x W x L / 2 ). For a gable roof, this will be reasonably accurate. For a hip roof house, the volume will be overestimated but adequate.*




All I want to know is what temperature to set the attic fans.


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## dustin

95 deg F


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## czygvtwkr

Depends how much you want them to run.  I set mine to 110.


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## ItalianScallion

I set both of mine to 95 degrees. On the hottest days (when it is 90 by 9am) it usually starts to run around that time. It is usually goes off @ 9pm. So it is like he said; it depends how long you want it to run. The higher the setting, the less it will run but the hotter the attic will be. I use a gable mounted fan not the "through the roof" type. I make sure to completely seal around the outer edges of the fan so that all of the air goes through the fan and doesn't get sucked in along side of it. Sorry for being long winded.


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## dn0121

Attic fans can do more harm then good.  For some great reading do a search on Radiant Barrier.  AtticFoil.com is a great place to get some info.  

Also check out these forums and do searches
Residential HVAC - HVAC-Talk: Heating, Air & Refrigeration Discussion
DoItYourself.com Community Forums - Home Improvement & Home Repair Questions & Answers


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